1. Field of the Invention
The present invention relates to an electrophotographic plate-making apparatus for transferring an image formed on a surface of a photosensitive material onto a recording material via an intermediate transfer material.
2. Description of the Related Art
As a method for making a machine plate for printing in an electrophotographic process, a method is known in which an image is formed on a photosensitive material by using a plate material coated with the photosensitive material, and the surface of the photosensitive material is then subjected to etching (Japanese Patent Application Laid-Open No. 63-163384). With this method, the accuracy of the position at which the image is formed is excellent since the plate material on which the image formed is subjected to etching. However, this method has a drawback in that high-alkali etching is required, so that the process is complicated and the running cost is high. As a method which is free from this drawback, a method is known in which an image formed on the photosensitive material is temporarily transferred onto an intermediate transfer material, and the image formed on the intermediate transfer material is further transferred onto a machine plate (Japanese Patent Application Laid-Open Nos. 62-81681 and 63-34572).
However, with the method using the intermediate transfer material, although the running cost does not become high since high-alkali etching is not required, it has been difficult to secure high positional accuracy required in color plate making and the like due to the large number of transfer processes. In particular, in a case where color-printing machine plates are made, it is necessary to make machine plates respectively corresponding to a black image, a yellow image, a magenta image, and a cyan image, so that high positional accuracy is required for the images formed on the respective machine plates.
In addition, at the time of transferring an image onto the intermediate transfer material and the machine plate, there have been cases where even if the positions of the intermediate transfer material and the machine plate are controlled by a high-accuracy encoder, the image is formed the proper position offset from a predetermined position on the intermediate transfer material due to the thermal expansion of the intermediate transfer material itself, the elongation of the transfer material, and the like. As a result, there have been cases where the image is not formed by the proper position at when the image is transferred onto the plate material.
As a method of forming an image on a machine plate with high positional accuracy, it has been the practice in the conventional field of printing to provide a register mark on an original plate at the time of preparing the original plate and to form the image on the machine plate by using the register mark as an index for registration. However, since the provision of the register mark is effected each time the original plate is made, a process for this purpose has had to be provided separately.
Meanwhile, as another method of forming an image on a machine plate with high positional accuracy, at the time of transferring the image formed on the photosensitive material onto the transfer material, it has been the practice in the conventional field of copying apparatus to eliminate the offsetting of colors by strictly effecting the registration of the photosensitive material with respect to the transfer material at the time of starting transfer. However, strict registration requires a complicated process.
Furthermore, in an electrophotographic plate-making apparatus using the intermediate transfer material, a shortcoming has been encountered with the durability of the intermediate transfer material since the image is transferred by bringing its surface into contact with the photosensitive material and the machine plate. In addition, replacing the intermediate transfer material is troublesome.